In temperate climate zones most fungal infections are caused by trichomycetes (dermatophytes), while in tropical climate zones, infections by yeast and molds are more common. Regardless of the cause of infection, the fungus attacks the nail and/or skin and makes it brittle and discolored.
There are four different types of nail infections caused by fungi. The most common infection is frequently caused by Trichophyton rubrum and affects the nail bed and the area beneath the nail. Another type of infection affects only the nail surface and creates white or light colored patches. This second type of fungal infection is unusual and represents only about 10% of the reported cases. A third type of fungal infection affects the nail root and usually afflicts persons with impaired immune defense. A fourth, unusual type is caused by an infection of yeast fungi. Infections by yeast most often only affect nails that already are infected or damaged in some way.
The fungi are invasive to the keratin nail tissue. Apart from becoming discolored and brittle, the nail may often separate from the nail bed. In addition, pain and difficulty in wearing foot apparel is often experienced. Initially, the disease affects only one nail, typically one nail of the foot, and is thereafter spread to more nails. The palms of the hands and the soles of the feet may frequently be affected as well. When the skin is affected, red spots frequently occur and the skin may peel off. Fungal infections of the skin and/or nail(s) are however not very contagious.
Nail fungal infections are one of the hardest forms of external infection to treat, of which infections of toe nails are the most difficult to treat. While current treatments are somewhat effective, they have adverse side-effects, and are contraindicated for patients taking certain drugs. For example, surgical removal of the nail or drilling holes in the nail to allow penetration of anti-fungal topical treatments results in considerable patient discomfort; systemic administration of anti-fungal drugs suffers from the inherent difficulties involved with parenteral administration and may also result in undesirable side-effects; and anti-fungal lacquers (painted on the nail) lack the necessary penetrating power to directly reach the fungal infection.
In U.S. 2002/0183387, one example of a composition for local administration is disclosed. The composition of U.S. 2002/0183387 has low viscosity and comprises an optionally substituted lower alcohol, such as methanol or ethanol, and an optionally substituted lower carboxylic acid, such as acetic acid or propionic acid, for treatment of bacterial or fungal infections of the nail. The composition, suitable for treatment of conditions such as onychomycosis, typically comprises about 50-90% alcohol by weight and about 10-40% carboxylic acid by weight. The composition penetrates through and underneath the nail plate, thereby attacking the infection.
Another example of a composition for local treatment of nail fungal infections is disclosed in EP 1 709 960. Therein, the composition comprises an alkanoic acid (e.g. methanoic acid) and water for treatment of fungal infections of nails. The preferred concentration ratio is one part acid to 16 parts warm water. The composition is administered by foot baths twice daily for 1-3 months. According to the applicants, the composition softens, dissolves and excoriates the surface and excess nail tissue known as keratin debris.
Other related compositions disclosed elsewhere include WO 2007/113830, U.S. Pat. No. 7,267,888, WO 2010/130028 and WO 00/45808.
Thus, there is still a need in the art for improved, simple and effective treatments of fungal infections of the skin and/or nails.